Cathode ray tube



L. E. FLORY ETAL CATHODE RAY TUBE Filed March 1, 1941 July 13, 1943.-

3nnentors ny, 8: A? than" WV. Va

LeaZie E Fl Patented July 13, 1943 CATHODE RAY TUBE I Leslie E. Flory,aklyn, and Arthur W. Vance,

Haddonfield, N. J., assignors to RadioCorporation of America, acorporation of Delaware Application March 1, 1941, Serial No. 381,216

2 Claims. (Cl. 250-161) This invention relates to thermionic dischargedevices and, more particularly, to electron beam tubes, and has for itsprimary object to provide an improved device and method of operation forproducing and controlling an electron beam.

In a cathode ray tube employing magnetic focussing use is usually madeof an accelerating electrode in close proximity to the thermionicemitter to accelerate the electrons away from the emitter or to act as amasking aperture or to provide both functions. When such an acceleratingelectrode is used, a sharp curvature of the equipotential surfaces isintroduced. This sharp curvature may give some of the electrons emittedfrom the cathode a high radial velocity producing a condition whichmakes it more difiicult to focus the electron beam. The primaryelectrons may also strike the edges of the apertures, giving rise tosecondary electrons which have a wide distribution in initial velocitiesand leave the aperture in random directions, resulting in furtherdifiiculties in focussing.

Another object of this invention is to eliminate the disturbance causedto the electron beam by the usual accelerating electrodes.

According to this invention, an extremely small electron source isprovided with a large cylindrical electron accelerating element suchthat the electron beam produced does not suffer from the limitationsintroduced by the presence of apertures or small accelerating electrodesand does not require any electrostatic or magnetic focussing means.

Other and incidental objects of this invention will be apparent to oneskilled in the art from a reading of the following specification takenin connection with the accompanying drawing in which- Figure .1 shows across-sectional view of one form of this invention, and

Figure 2 is a cross-sectional view of a modification of Fig. 1.

Referring in more detail to Figure 1, an envelope I contains a heaterelement 3 which is enclosed in a cathode member 5 having therein a verysmall point of electron-emissive material I. The structure of thecathode may take the form as shown and described in more detail in theGeorge Patent 2,117,842 of May 17, 1938. A disc element 9 extendsoutwardly from the cathode.

A large cylindrical accelerating electrode I I takes the form of aconducting coating flashed on the inner surface of the envelope I or itmay be a cylinder supported adjacent the walls of the envelope I suchthat it extends'between the cathode I and the target electrode I3. Thetarget electrode I3 comprises a translucent member supportingphotoactive material I5. The target electrode I3 may take the form shownand described in the patent to Rose 2,213,174 of August 27, 1940.

Vertical deflecting coils I! are provided such that the electron beammay be scanned in the vertical direction and similar deflecting coils I8are provided for deflecting the electron beam in the horizontaldirection.

A coaxial coil I9 is provided to maintain the electrons emitted from thepoint source I along in a beam which may be controlled by the defiectioncoils I! and I8.

In the operation of the device, the cathode 5 may be either directly orindirectly heated. As the electron-emissive material I is heated,electrons tend to be emitted in all directions forward from the cathode5. However, the magnetic field from the coil I9 causes the electronsemitted from the electron emissive source 1 to follow in a beam whosediameter remains substantially uniform and would normally follow alongthe axis of the uniform magnetic field produced by the coil IS.

The disc 9, which surrounds the cathode 5, leaving only a small area ofthe cathode exposed in the direction of the travel of the beam, isprovided with a potential substantially equal to that of the cathode 5.The large cylindrical accelerating electrode II is charged with apositive potential such that it produces an electric field adjacent thecathode which is practically fiat, so that the electrons from theemissive point source 1 are accelerated only axially. As a result, theonly radial velocity of the electrons is that due to the initialvelocities of thermionic emission, the efiect of which is counteractedby the field from the coil I9.

A predetermined wave form may be applied to the deflecting coils I1 andI8 such that the electron beam will scan the mosaic electrode I3 at apredetermined rate.

If more than one large accelerating electrode is used, it is preferablethat these be connected to increasing positive potentials until themaximum beam velocity is reached. Fig. 2 is a fragmentary view of thedevice, wherein a plurality of accelerating electrodes, 2|, 22, 23, 24are shown connected to progressively higher positive potentials derivedfrom the source 25. Beyond this point in the tube, the beam may beallowed to strike a target such as shown by the target electrode I3, ora luminescent screen may be substituted. Instead of allowing the beam tostrike the mosaic electrode I3 shown, at high velocity it may first bedecelerated and utilized as a low velocity beam such as in the negativeequilibrium type of Iconoscope otherwise known as Orthicon.

For the purpose of explanation, magnetic deflection has been shown.However, electrostatic deflection may be substituted without departingfrom the spirit of this invention.

While one system for carrying this invention into effect has beenindicated and described, it will be apparent to one skilled in the artthat this invention is by no means limited to the particularorganization shown and described, but that many modifications may bemade without departing from the scope of this invention as set forth inthe appended claims.

We claim as our invention:

1. In combination, a thermionic tube including an element for producingelectron rays by thermionic emission, magnetic means for maintainingsaid rays in a beam whose cross-sectional area remains substantiallyconstant throughout its length and Whose crosssectional area issubstantially equal to the area of the electron-emissive area of saidelement, a target for said beam, means for causing said beam to scansaid target, means for producing an electric field of increasingpotential in a direction away from said element and whose equalpotential areas are substantially flat in the region of the electronbeam throughout its scanning range.

2. A thermionic tube including an electron emissive area for producingelectron rays by thermionic emission, means for producing asubstantially uniform magnetic field about said rays to concentrate saidrays in an electron beam having a substantially uniform cross-sectionalarea and whose cross-sectional area is substantially equal to the areaof said electron emissive area, a target for said beam, means forcausing said beam to scan said target, and means for producing anelectric field whose equal potential areas are substantially flat in theregion of the electron beam throughout its scanning range.

LESLIE E. FLORY. ARTHUR W. VANCE.

